Exhaust-gas turbocharger having a wastegate device

ABSTRACT

The invention relates to an exhaust-gas turbocharger for an internal combustion engine ( 1 ), having a turbine ( 2 ), having a compressor wheel ( 4 ), which is connected to said turbine by means of a shaft, and having a wastegate device ( 8 ), which wastegate device has a wastegate actuator ( 5 ), has a wastegate drive shaft ( 7 ) rotatable about an axis of rotation ( 6 ), and has a flap ( 20   a,    20   b,    20   c,    20   d,    20   e,    20   f,    20   g ) which is fastened to said drive shaft and which is pivotable about the axis of rotation and which has a covering surface ( 9 ) for potentially opening up and closing off a wastegate opening ( 10   a ), wherein the wastegate flap and the wastegate opening ( 10   a ) that can be closed off by means of said wastegate flap are designed in such a way that the distance between the center of area ( 11, 1   a ) of the covering surface ( 9 ), which covers the wastegate opening, of the wastegate flap and the axis of rotation ( 6 ) is smaller than the radius of a circular surface of equal surface area.

The invention is within the field of mechanical engineering and can beused with particular advantage in automotive engineering. Morespecifically, the invention relates to an exhaust-gas turbocharger.

To increase the utilization of the fuel and to boost power and ensureeconomical and environmentally friendly operation, many modern internalcombustion engines have an exhaust-gas turbocharger. A turbocharger ofthis kind has, in the exhaust gas flow of the internal combustionengine, a turbine that can be driven by this exhaust gas flow and acompressor, which is arranged in the induced gas flow and whichcompresses the induced air fed to the internal combustion engine. Theexhaust-gas turbine and the compressor are connected to one another bymeans of a shaft, with the result that the turbine drives the compressorwheel.

For improved control of the exhaust gas flow, a wastegate opening isprovided from the exhaust side of the internal combustion engine, in theregion of the turbine, which wastegate opening provides a bypass channelfor the exhaust gas flow and can be closed in a controlled manner bymeans of a wastegate flap. Depending on the operating conditions, theexhaust gas flow can thereby be fed in whole or in part to the turbineof the turbocharger. Control of the wastegate flap is usuallyaccomplished mechanically by means of a control rod, which can be drivenby an actuator. By means of a lever, the control rod usually drives awastegate spindle or wastegate shaft, on which the wastegate flap issecured within the turbocharger device.

An important requirement of the wastegate system is that the wastegateflap can be closed and held closed reliably against the exhaust gaspressure. Compliance with this requirement depends essentially on thebalance of forces acting on the wastegate flap. Said wastegate flap isacted upon, on the one hand, by the exhaust gas pressure and, on theother hand, by the contact pressure provided by the torque of the shaft.For reliable and firm closing of the flap, it is necessary that theforce acting on the flap via the shaft is greater than the exhaust-gasforce. To increase the contact force, either the chosen driving lever ofthe wastegate shaft outside the turbine casing can be particularly largeand/or the chosen distance between the wastegate flap and the axis ofrotation can be as small as possible.

Accordingly, it is the underlying object of the present invention toconfigure an exhaust-gas turbocharger of the type stated at the outsetin such a way that the contact pressure on the wastegate flap becomes aslarge as possible.

The object is achieved by means of the features of the invention inaccordance with patent claim 1.

Accordingly, the invention relates to an exhaust-gas turbocharger for aninternal combustion engine, having a turbine, having a compressor wheel,which is connected to said turbine by means of a shaft, and having awastegate device, which wastegate device has a wastegate actuator, has awastegate drive shaft rotatable about an axis of rotation, and has aflap, which is fastened to said drive shaft and which is pivotable aboutthe axis of rotation and which has a covering surface for potentiallyopening up and closing off a wastegate opening, wherein the wastegateflap and the wastegate opening that can be closed off by means of saidwastegate flap are designed in such a way that the distance between thecenter of area of the covering surface, which covers the wastegateopening, of the wastegate flap and the axis of rotation is smaller thanthe radius of a circular surface of equal surface area.

The contact pressure of the wastegate flap on the wastegate opening oron the sealing edge of the opening depends on the average distancebetween the sealing edge of the wastegate flap forming the boundary edgeof the covering surface and the axis of rotation. This quantity can bedescribed by the position of the center of area relative to the axis ofrotation. For example, the center of area of the covering surface of thewastegate flap can move closer to the axis of rotation if the coveringsurface is extended in length parallel to the axis of rotation andcompressed transversely to the axis of rotation, starting from aconstant size of the covering surface. Given a constant size of theopening or covering surface, the contact pressure of the wastegate flapon the wastegate opening can therefore be increased by means of thestated shaping of the covering surface.

A particularly advantageous possibility here is to provide for thewastegate flap and the wastegate opening that can be closed by said flapto be designed in such a way that the minimum distance between thecovering surface and the axis of rotation is as small as possible.

In the case of a circular configuration of the covering surface of thewastegate flap, this is advantageously spaced apart from the axis ofrotation to such an extent that the minimum distance between thecovering surface and the axis of rotation corresponds to the magnitudeof a tolerance, with the result that, even when the tolerance is fullyexhausted, the entire covering surface is on one side of the axis ofrotation and the wastegate opening can be fully opened when thewastegate flap is swung open.

The invention can furthermore advantageously provide for the coveringsurface to have at least one straight edge, which is, in particular,parallel to the axis of rotation or encloses with the latter an anglewhich is less than 10 degrees. Such an edge can form thecovering-surface lateral edge facing the axis of rotation, for example,or can form the side facing away from the axis of rotation.

It is also advantageously possible to provide for the covering surfaceto have at least two straight edges, wherein the two edges are, inparticular, parallel to one another or enclose between them an anglewhich is less than 10 degrees.

The covering surface can be irregularly shaped but bounded by straightlines or irregularly shaped and bounded by irregular lines. For example,it can have an edge on the side facing the axis of rotation which issubstantially parallel to the axis of rotation and a parallel edge onthe covering-surface side facing away from the axis of rotation. If thecovering surface has an edge which is straight and parallel to the axisof rotation on its side facing the axis of rotation, then, according toplan, this edge should be spaced apart from the axis of rotation by atleast the tolerance spacing.

The covering surface can be of triangular, rectangular, trapezoidal,elliptical or diamond shape. In the case of an elliptical or diamondshape, this should be extended parallel to the axis of rotation andcompressed perpendicularly thereto. For example, the covering surfacecan be of mirror-symmetrical configuration relative to an axisperpendicular to the axis of rotation. The corresponding sealing surfaceat the wastegate opening should then have a corresponding shape in eachcase.

Provision can furthermore advantageously be made for the sealing surfaceof the flap, said sealing surface surrounding the covering surface, tobe flat and parallel to the plane of the sealing surface.

This makes possible secure and reliable sealing of the covering flapunder the influence of the contact force, even against a gas pressure.

Another advantageous embodiment of the invention envisages that thesealing surface of the flap, said sealing surface surrounding thecovering surface, slopes relative to the covering surface.

If the sealing surface slopes relative to the covering surface at thecovering surface, centering of the wastegate flap on the wastegateopening can be achieved by means of the transverse forces which actduring the closure of the flap, and therefore better sealing and hencebetter efficiency of the exhaust-gas turbocharger can be achieved. Inthis case, all the regions of the sealing surface around the coveringsurface can either all have the same slope toward the inside of thecovering surface or all have the same slope outward away from thecovering surface.

The invention can also advantageously be configured in such a way thatthe sealing surface of the flap, said sealing surface surrounding thecovering surface, is of conical or spherical-cap-shaped design. Aconical or spherical-cap configuration of the sealing surface around thecovering surface allows particularly efficient sealing and centering ofthe wastegate flap in the wastegate opening.

Provision can furthermore advantageously be made for the coveringsurface to have a projection which extends into the wastegate openingduring closure. The provision of such a projection facilitates guidanceof the flow during the opening of the flap and the configuration of afree channel when the wastegate flap is open.

Provision can furthermore advantageously be made for the thickness ofthe projection to increase with increasing distance from the axis ofrotation, starting from the region of the wastegate flap which isclosest to the axis of rotation. By means of such a configuration of theprojection on the wastegate flap, it is ensured that the projection doesnot constitute an obstruction at the edge of the wastegate opening inthat region of the wastegate flap which is close to the axis ofrotation, especially at the beginning of the opening movement or at theend of the closing movement.

In the following part of the document, the invention is illustrated infigures of a drawing by means of illustrative embodiments and thenexplained. In the drawing:

FIG. 1 shows a schematic illustration of the functional elements of anexhaust-gas turbocharger,

FIG. 2 shows a perspective view of an exhaust-gas turbocharger inpartial section,

FIG. 3 shows a view of the control rod of the exhaust-gas turbochargerin the upper area of the illustration, while a section along the lineA-A in the upper part is illustrated in the lower area,

FIG. 4 shows a partially sectioned illustration of the wastegate flapwith the drive shaft thereof,

FIG. 5 shows a schematic illustration of the wastegate flap with thedrive shaft thereof,

FIG. 6 shows another schematic illustration of the wastegate flap,

FIG. 7 shows a schematic illustration of a wastegate flap in triangularform,

FIG. 8 shows a schematic illustration of a wastegate flap in rectangularform,

FIG. 9 shows a schematic illustration of a wastegate flap in a flattenedpartially circular form,

FIG. 10 shows the illustration of four further geometrical shapes ofwastegate flaps,

FIG. 11 shows three views of a round wastegate flap in variousperspectives,

FIG. 12 shows three views of another wastegate flap in variousperspectives,

FIG. 13 shows the view of a triangular wastegate flap with a raisedportion on the inner side,

FIG. 14 shows three views of a wastegate flap in the form of a circulardisk with a conical sealing surface,

FIG. 15 shows three views of a flattened wastegate flap in the form of apartial circle with a spherical-cap-shaped sealing surface,

FIG. 16 shows a view of a flattened wastegate flap in the form of apartial circle with the drive shaft thereof, and

FIG. 17 shows a cross section along the line B-B in FIG. 16.

FIG. 1 illustrates schematically the elements of an exhaust-gasturbocharger. This is structurally connected to an internal combustionengine 1, which has an intake duct 1 a and an exhaust duct 1 b. Ambientair for combustion is drawn in through the intake duct 1 a, while thecombustion products heated up during the combustion process, principallyin gas form, are expelled through the exhaust duct 1 b.

Arranged in the exhaust duct 1 b is a turbine 2, which is driven by theexpelled exhaust gases. This is connected by means of a shaft 3 to acompressor wheel 4. During the operation of the turbocharger device, thecompressor wheel 4 is driven in such a way that it additionallycompresses the air drawn in through the intake duct 1 a, with the resultthat compressed intake air is available for the combustion process andmore fuel can be added to it per cylinder stroke, thus allowing theengine torque to be increased.

A throttle valve 1 c for controlling the intake air, an air filter (notshown) ahead of the compressor wheel, as well as an air flow meter aheadof the compressor wheel and a charge air cooler downstream of thecompressor wheel are provided in the intake duct 1 a. Also worthmentioning is the possible arrangement of a catalytic converter in theexhaust duct 1 b downstream of the turbine 2.

In the pressure-charged mode, the throttle valve 1 c is fully open.

Regulation of pressure charging is possible by releasing some of theexhaust gas mass flow on the turbine side through the “wastegate” 10with a wastegate opening, thereby opening a bypass duct which makes itpossible to guide some of the exhaust gases past the turbine 2.

FIG. 2 shows, in a perspective view, the turbine casing 15, in which thewastegate device 10 is arranged. Said device is actuated by means of anelectric wastegate actuator 5, which is mounted on a holder on thecompressor casing 14. Between the turbine casing 15 and the compressorcasing 14 there is a core group, in which the common shaft of theexhaust-gas turbine and of the compressor wheel is accommodated. Theexhaust-gas turbine 2 can be seen in the foreground.

The control rod of the actuator 5 is denoted by 5 a. As elements, as canbe seen in FIG. 3, it has a tappet 18, which can be moved in thelongitudinal direction thereof, as well as a joint 16 and an extension17, which is coupled to the lever 19 of the wastegate drive shaft 7. Thejoint 16 is required to compensate for the circular movement of thelever 7 since the tappet 18 can only move axially. By means of theactuator 5, the shaft 7 can thus be driven in rotation as a drive shaftof the wastegate flap.

The section line A-A, along which a cross section is shown in the lowerpart of FIG. 3, is indicated in the upper half of FIG. 3. The crosssection shows part of the turbine casing 15 with the wastegate flap 8and the wastegate drive shaft 7. The tappet 18, the joint 16 and theextension 17 of the control rod 5 a can also be seen in the lower partof the figure.

The force relationships between the forces acting on the wastegate flap8 are illustrated in FIG. 4. Acting in the direction of arrow 20 thereis first of all the actuating force 20, which is transmitted to the flap8 by the control rod 5 a and the drive shaft 7. Acting as counter forcesthere are force 21, which is produced by the gas pressure in thewastegate device, and force 22, which forms the pressing force on theseal seat of the wastegate opening. If the force on the seal seat is tobe as large as possible, it would seem advisable to maximize the forcetransmitted to the flap by the drive shaft.

For this purpose, as can easily be seen in FIG. 5, it is particularlyadvantageous if the load arm L between the center of area 11 and theaxis of rotation 6 of the drive shaft 7 is as short as possible. Forthis purpose, it is advisable to position the covering surface of thewastegate flap 8 as close as possible to the axis of rotation 6. Thisgives rise to a large torque on the flap, thereby making it possible toproduce a large contact force on the seal seat. At the same time,however, it should be taken into account that, in some cases, the flap 8should be at a minimum distance from the axis of rotation 6, in the formof tolerance length a, in order to compensate for tolerances. If thetolerance were not respected and the lever arm L became too short, thewastegate flap would strike against the seat on the wastegate openingbefore the closed flap position was reached. With modern manufacturingmethods, however, the tolerance can be reduced virtually to zero.

FIG. 6 shows in greater detail that the wastegate flap 8 overall has alarger diameter than the covering surface, which is illustrated in acircle of dashed lines and is denoted by 9. The covering surface coversthe wastegate opening within the sealing surface.

FIG. 7 shows an illustration according to the invention of a wastegateflap 20 a, the center of area 11 a of which is positioned closer to theaxis of rotation 6 in comparison with a circular configuration of thecovering surface, while the surface area is the same. This isaccomplished by means of a triangular configuration, wherein thetriangle is configured in such a way that a straight edge 21 a runsparallel to the axis of rotation 6. According to the rules of geometry,the center of area is arranged at one third of the height of thetriangle in relation to the edge 21 a, as viewed from the axis ofrotation 6.

FIG. 8 shows a rectangular wastegate flap 20 b, on which an edge 21 b ofthe covering surface is arranged parallel to the axis of rotation 6. Therectangle 20 b and the corresponding covering surface are extended in adirection parallel to the axis of rotation 6 and compressedperpendicularly thereto.

FIG. 9 shows a wastegate flap 20 c in a flattened circular shape,wherein an edge 21 c of the covering surface, once again illustrated indashed lines here, is parallel to the axis of rotation 6 on the sidefacing the latter. The covering surface of this wastegate flap 20 c iscomparable in respect of surface area to a circular wastegate flap witha circular covering surface of smaller diameter. By virtue of the flatin the region of edge 21 c, the wastegate flap 20 c and hence also thecovering surface can be positioned closer to the axis of rotation 6while being of the same size, and therefore a higher contact force ofthe flap 20 c on the seat of the wastegate opening can be achieved forthe same torque of the shaft 7. The illustrated flattened configurationof the wastegate flap 20 c is extended in a direction parallel to theaxis of rotation 6 and compressed transversely thereto in comparisonwith a corresponding circular shape.

FIG. 10 shows four further configurations of wastegate flaps 20 d(elliptical, wherein the long axis of the ellipse is aligned parallel tothe axis of rotation 6), 20 e (trapezoidal, wherein the longer side ofthe trapezoid faces the axis of rotation), 20 f (diamond-shaped, whereinthe long axis of the diamond is aligned parallel to the axis ofrotation) and 20 g (irregularly shaped with a configuration which isextended in the direction of the axis of rotation 6 in comparison with acircular surface). Other geometrical shapes of wastegate flaps withcorresponding covering surfaces are conceivable within the scope of theinvention.

FIG. 11 shows a drive shaft 7 for a wastegate flap 8 in three differentperspective views, said flap having a circular covering surface 9. Thecircular shaping does not correspond to the shape envisaged according tothe invention but this example is a simple means of illustrating theprovision of a projection on the wastegate flap. The simplest example ofthe projection can be seen in the central illustration since it extendsbeyond the flat annular outer part of the sealing surface 22 of thewastegate flap disk. During the closure of the wastegate opening 10 a,the projection 24 enters said opening. The projection 24 is of conicalconstruction in order to shape the opening characteristic of thewastegate valve since this shaping ensures that a reduced cross sectionis available in a partially open position of the flap. In the firstphase of opening, only a small flow cross section is thus initiallyexposed in comparison with the full pivoting angle of the wastegateflap, and this initial displacement is subsequently completed as theopening angle increases until the wastegate opening is fully exposed.

A corresponding configuration of projections 24 a, 24 c can also befound in FIGS. 12 and 13.

FIG. 12 shows a wastegate flap 20 c in a triple perspective view, saidflap being partially circular but flattened by means of the edge 21 c inthe region close to the axis of rotation 6. In the central illustrationin FIG. 12, the conically tapering projection 24 c can be seen, saidprojection rising above the sealing surface 22. The drive shaft 7 andthe load lever 23 are furthermore illustrated in FIG. 12.

FIG. 13 shows a triangular wastegate flap 20 a in a perspectiveillustration, said flap having a projection 24 a which is constructed inthe manner of a wedge from the edge 25 close to the axis of rotation ofthe triangular wastegate flap toward the pointed end 26. Thisconfiguration further improves the opening characteristic of thewastegate valve, i.e. of the free flow cross section relative to theopening angle of the wastegate flap. Such an oblique rise in theprojection across the width of the wastegate flap can of course also beappropriate in the case of other geometries.

FIG. 14 shows a round wastegate flap 8 in a corresponding drive shaft 7in a triple perspective view. As is clearly visible in the central view,the wastegate flap has a conical shape in the region of the valve seat,i.e. in the region of the sealing surface of the valve flap whichinteracts with the edge of the wastegate opening. This has the effectthat the wastegate flap disk is centered automatically on the wastegateopening and that the seal between the wastegate flap and the edge of thewastegate opening is improved.

FIG. 15 shows a similar wastegate flap to that in FIG. 14 in a tripleperspective view, although the contour 26 of the sealing surface of thewastegate flap is of spherical-cap-shaped construction, i.e. has aspherical curvature.

FIG. 16 once again shows a flattened circular wastegate flap 8 togetherwith the load lever 23 and the shaft 7. In FIG. 16, B-B furthermoreindicates a section which is illustrated in FIG. 17. There, thewastegate flap 8 is shown in cross section with a conical sealingsurface 27, which rests against a correspondingly conically recessedwall 15 a of the turbine casing 15, in which the wastegate opening 10 ais provided. The edge 28 of the wastegate opening is complementary indesign to the conical shape of the wastegate flap 8, giving rise to avalve seat that provides a good seal. This complementary shaping of theedge of the wastegate opening and the wastegate flap is also notrestricted to circular wastegate flaps and to a conical shape but canalso be provided for all the flap shapes presented.

In the end, an increased contact pressure of the wastegate flaps andhence better sealing behavior of the wastegate valve and thereforebetter efficiency of the exhaust-gas turbocharger and of the combustionengine can be achieved with the flap shapes shown and explained above.

1. An exhaust-gas turbocharger for an internal combustion engine,comprising a turbine, a compressor wheel connected to said turbine by ashaft, and comprising a wastegate device, the wastegate devicecomprising a wastegate actuator, has a wastegate drive shaft rotatableabout an axis of rotation, and has a flap, the flap fastened to saiddrive shaft and pivotable about the axis of rotation and defining acovering surface for potentially opening up and closing off a wastegateopening, wherein at least one of the wastegate flap and the wastegateopening that may be closed off by means of said wastegate flap areconfigured in such a way that the distance between the center of area ofthe covering surface, configured to cover the wastegate opening, of thewastegate flap and the axis of rotation is smaller than the radius of acircular surface of equal surface area and the covering surface of thewastegate flap and the wastegate opening that can be closed off by meansof said wastegate flap are extended in a direction parallel to the axisof rotation and compressed perpendicularly to the axis of rotation incomparison with a circular configuration of equal surface area. 2.(canceled)
 3. The exhaust-gas turbocharger as claimed in claim 1,wherein the minimum distance between the covering surface and the axisof rotation amounts to a tolerance length.
 4. The exhaust-gasturbocharger as claimed in claim 1, wherein the covering surface atleast one of defines at least one straight edge and the covering surfacedefines at least two straight edges.
 5. (canceled)
 6. The exhaust-gasturbocharger as claimed in claim 4, wherein one straight edge of thecovering surface is situated at a covering-surface end facing the axisof rotation.
 7. The exhaust-gas turbocharger as claimed in claim 1,wherein the covering surface is of triangular, rectangular, trapezoidal,elliptical or diamond shape.
 8. The exhaust-gas turbocharger as claimedin claim 1, wherein the covering surface defines a projection, whichextends into the wastegate opening during closure.
 9. The exhaust-gasturbocharger as claimed in claim 1, wherein the sealing surface of theflap, the sealing surface surrounding the covering surface, is flat andparallel to the plane of the covering surface.
 10. The exhaust-gasturbocharger as claimed in claim 1, wherein the sealing surface of theflap, said sealing surface surrounding the covering surface, slopesrelative to the covering surface.
 11. The exhaust-gas turbocharger asclaimed in claim 1, wherein the sealing surface of the flap, saidsealing surface surrounding the covering surface, is conical- orspherical-cap-shaped.
 12. The exhaust-gas turbocharger as claimed inclaim 1, wherein the covering surface has a projection which extendsinto the wastegate opening during closure.
 13. The exhaust-gasturbocharger as claimed in claim 11, wherein the thickness of theprojection increases with increasing distance from the axis of rotation,starting from the region of the wastegate flap closest to the axis ofrotation.
 14. The exhaust-gas turbocharger as claimed in claim 4,wherein at least one of: the at least one straight edge is parallel tothe axis of rotation or encloses with the latter an angle which is lessthan 10 degrees, and the two edges are parallel to one another orenclose between them an angle which is less than 10 degrees.
 15. Theexhaust-gas turbocharger as claimed in claim 8, wherein the projectionis configured to correspond to the wastegate opening to be covered.